I can't answer what Bombadil is in the lore of LOTR, he seems to be unique in terms of entities we are shown. But I can tell you what he is at a meta level. You see, LOTR was first told as stories to Tolkiens kids, which you probably already knew, which you may not have known, is that Bombadil was a recurring character in previous stories he had told his children. So at a meta level, Bombadil is just a fun callback to a previous character for his kids to have enjoyed.

I believe he is considered the spirit of that world, not necessarily a god, but a physical incarnation of the world. It would explain why he holds an insane amount of power and even Sauron’s ring only tickled him. It also makes sense when Gandalf says if Mordor conquers the rest of the world then maybe bombadil would fall because the world would be irreparably harmed

As far as I know Tom is left as an enigmatic character and never explained. Just a strange encounter to make the world seem larger and more mysterious.

He’s Q but it’s TLOTR

He’s a merry fellow, bright blue his jacket is and his boots are yellow.

Tom represents the incomplete knowledge of mankind and our pre-modern inability to firmly grasp the natural world we live in (and to some extent our continued struggle).

The fantasy world of Middle-Earth is in most ways supernatural to our own. So how much more incomplete would our understanding and knowledge of it been?

Tolkien was a professor of language and mythology and steeped in the ancient epics of the Anglo-saxons and Norse cultures. His career was putting together what these people knew and how they saw the world, but also what they couldn't understand and how they explained their ignorance.

Others here are hinting at what Tom is, but not why he is. He's a manifestation of ignorance. That's why pinning him down is so tricky. It's like pointing at a shadow with a flashlight.

He is a character who is not connected to the main conflict in the story in any way, and is meant to show that the world of middle earth is much larger and more mysterious than what the hobbits/men/elves/orcs are fighting over. His back story was left as a mystery on purpose. The simplest explanation to accept is that you’re just not supposed to know.

There is a whole lot of fan theory and actual letters from Tolkien himself explaining (or rather not explaining) the character.

Some had suggested he was the spirit of "JRR Tolkien" placed into his own book

A merry fellow, of course, he says so right in his song

Old Tom Bombadil is a merry fellow, Bright blue his jacket is, and his boots are yellow. None has ever caught him yet, for Tom, he is the master: His songs are the stronger songs, and his feet are faster.

He's just a supremely powerful being (nameless thing, perhaps) who was created at the same time as Arda and who is just content living in a forest singing all day about how hot his wife is instead of caring about anything that happens in the world around him.

The question is, what is his wife, Goldberry? She appears to be a personification of nature, Arda, or just the Old Forest or something.

@TomBombadil@hexbear.net , A statement please.

a nature spirit, yeah?

Old primordial nature spirit that is a physical manifestation of the worlds untamed wilderness and magical possibility

You got some great answers already here. I'll just say that according to Wizards of the Coast he is a God.

"Eldest, that's what I am... Tom remembers the first raindrop and the first acorn... He knew the dark under the stars when it was fearless - before the Dark Lord came from Outside."

https://tolkiengateway.net/wiki/Tom_Bombadil

I like the theory that he is Eru Iluvatar.

the Navajo had a tradition of weaving a single, intentional imperfection into the patterns on their blankets and rugs.. they said it was so that their spirit didn't get trapped inside the weave..

Freelance heating engineer.

Tolkien was just retelling legends, folktales, fairy tales, children's bedtime stories etc. He did piece them together to create extended connected lore, but not everything gets cleanly explained away in this kind of worldbuilding technique.

So really imo Tom Bombadil is just some contrivance of Tolkien to make the story feel more like some old fairy tale.

In deep geek has a neat video about Tom Bombadil, if you're into that kind of thing.

He's just this guy, you know?

A druidic forest spirit.

Maybe he's a demi-god whose back story we don't know enough about.

Gandalf seems pretty human to start with, but then we find out that he's a superhuman/demigod. That whole circle of wizards seems superhuman.

What was Sauron?

I think CS Lewis and Lewis Carroll had a better approach of just being like "Look, anything we want can show up as part of the story."

Tolkien had to create all of these taxonomies, bloodlines, and typing, which is why we're talking about this.

He's a cool dude